Light emitting diode and forming method thereof

ABSTRACT

A light emitting diode (LED) and a forming method thereof are provided. The LED includes a semiconductor substrate, a bonding layer formed on a surface of the semiconductor substrate, and a LED die formed on a surface of the bonding layer. The effective lighting area of the LED may be increased, heat radiation may be improved, and lighting efficiency may be enhanced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 13/881,723, entitled “LIGHT EMITTING DIODE AND FORMING METHODTHEREOF”, filed on Jul. 12, 2013, which is a Section 371 National StageApplication of International Application No. PCT/CN2011/070901, filed onFeb. 10, 2011, which claims priority to Chinese patent application No.201010523853.5, filed on Oct. 28, 2010, and entitled “LIGHT EMITTINGDIODE AND FORMING METHOD THEREOF”, and the entire disclosures of whichare expressly incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to semiconductor lightingfield, and more particularly, to a light emitting diode and a formingmethod thereof.

BACKGROUND OF THE DISCLOSURE

A semiconductor Light Emitting Diode (LED) is a solid semiconductorlight emitting device, which uses a solid semiconductor chip as a lightemitting material and releases surplus energy by means of recombinationof charge carriers, thus leading to photon emission and directlygenerating light like red, yellow, blue, green, cyan, orange and purplelight.

According to emitting colors, LED can be divided into two groups,monochrome LED and white light LED. In the 1980s, a super highbrightness red LED was invented. The early red LED was grown on a lightabsorption substrate and its light emitting efficiency was 1-2lumens/watt. Later, improvements are made to the red LED by using atransparent substrate. Among all the super high brightness red LEDs, thebest model had a light emitting efficiency of about 9 lumens/watt, withits emitting wavelength about 640 nm and drive current ranging from 30mA to 50 mA. When given a voltage of 1.5V, the best model emitted gloomylight. Afterwards, a high-efficiency red LED, a high-efficiencyorange-red LED and a high-efficiency orange LED formed on a galliumphosphide (GaP) substrate were developed. And a high brightnessorange-red LED, a high brightness orange LED and a high brightnessyellow LED were developed. The first green LED was formed by usinggallium phosphide, which had a light emitting efficiency of tens oflumens per watt and the maximum drive current of 30 mA. Afterwards, ahigh-efficiency green LED and a green LED emerged. The firsthigh-brightness wide-waveband gallium nitride (GaN) blue LED wassuccessfully developed by Nichia in the 1990s, which had an opticalspectrum spanning areas of purple, blue and green, and had a peak widthof 450 nm. The first high brightness silicon carbide (SiC) blue LED wassuccessfully developed by Cree in the 1990s. The first high brightnesssilicon carbide blue LED had a very wide optical spectrum range, andmore particularly, had a large intensity in an optical spectrum rangefrom mid-blue to purple. The peak width of the first high brightnesssilicon carbide blue LED ranged from 428 nm to 430 nm and the maximumdrive current was about 30 mA, generally, 10 mA was used.

FIG. 1 schematically illustrates a structure of a monochrome LED in theexisting methods. Hereinafter, a blue LED is taken as an example.Referring to FIG. 1, a buffer layer 11 made of n-doped gallium nitride(n-GaN) is formed on a sapphire substrate (Al₂O₃) 10; a multi-quantumwell active layer 12 made of indium gallium nitride (InGaN) is formed onthe buffer layer 11 and a cap layer 13 made of p-doped gallium nitride(p-GaN) is formed on the multi-quantum well active layer 12. The bufferlayer 11, the multi-quantum well active layer 12 and the cap layer 13collectively form a LED die. Besides, a transparent metal contact layer14 is formed on the cap layer 13. A positive electrode 15 iselectrically connected to the cap layer 13. In order to expose thebuffer layer 11, a groove 16 is formed extending through the metalcontact layer 14, the cap layer 13, the multi-quantum well active layer12 and the buffer layer 11. A negative electrode 17 is formed on thebottom of the groove 16 and is electrically connected to the bufferlayer 11. Thus, a voltage can be applied to the LED die through thepositive electrode 15 and the negative electrode 17 to cause the LED toemit light.

In the prior art, a sapphire substrate 10 is generally employed to forma LED. Since the material of the sapphire substrate 10 is insulative, itis necessary to form a groove 16 and expose a buffer layer 11 through anegative electrode 17. The groove 16 may reduce an effective emittingarea of the LED.

SUMMARY

Embodiments of the present disclosure provide a LED and a forming methodthereof. The forming method may increase an effective emitting area ofthe LED.

In an embodiment, a method for forming a LED may include steps of:

providing a semiconductor substrate;

forming a first bonding layer on the semiconductor substrate;

providing a sapphire substrate;

forming a sacrificial layer, a LED die and a second bonding layersuccessively on the sapphire substrate;

bonding the first bonding layer and the second bonding layer; and

removing the sacrificial layer and peeling the sapphire substrate.

Optionally, the method for forming a LED may further include: forming aconnection electrode on a surface of the LED die exposed from peelingthe sapphire substrate.

Optionally, the sacrificial layer may have a thickness ranging from 10nm to 50 nm.

Optionally, the sacrificial layer may be made of boron phosphide (BP).

Optionally, removing the sacrificial layer may include: removing thesacrificial layer through an etching process by employing a hydrochloricacid gas.

Optionally, a first buffer layer may be formed between the sapphiresubstrate and the sacrificial layer.

Optionally, the first buffer layer may be made of aluminum nitride(AlN).

Optionally, the first bonding layer may be made of palladium and thesecond bonding layer may be made of indium or silver.

Optionally, the first bonding layer may be made of palladium and thesecond bonding layer may be a laminated construction of indium andpalladium or a laminated construction of silver and palladium.

Optionally, the first bonding layer may be made of palladium and thesecond bonding layer may be a single layer of indium or a laminatedconstruction of indium and palladium. The bonding process of the firstbonding layer and the second bonding layer may have a reactiontemperature ranging from 180° C. to 220° C.

Optionally, a contact electrode layer may be formed between the secondbonding layer and the LED die.

Optionally, the contact electrode layer may be made of titanium.

Optionally, the contact electrode layer may have a thickness rangingfrom 2 nm to 10 nm.

Optionally, the LED die may include a cap layer, an active layer and asecond buffer layer which are formed successively on the sacrificiallayer.

Optionally, the semiconductor substrate may be an n-doped siliconsubstrate.

In an embodiment, a LED may include:

a semiconductor substrate;

a bonding layer formed on a surface of the semiconductor substrate; and

a LED die formed on a surface of the bonding layer.

Optionally, a connection electrode may be formed on a surface of the LEDdie.

Optionally, the bonding layer may be made of palladium indium alloy(PdIn₃) or palladium-silver (PdAg).

Optionally, a contact electrode layer may be formed between the bondinglayer and the LED die.

Optionally, the contact electrode layer may be made of titanium.

Optionally, the contact electrode layer may have a thickness rangingfrom 2 nm to 10 nm.

Optionally, the LED die may include a buffer layer, an active layer anda cap layer which are formed successively on the bonding layer.

Optionally, the semiconductor substrate may be an n-doped siliconsubstrate.

Compared with the existing methods, the present disclosure may havefollowing advantages.

In the method for forming a LED in the present disclosure, asemiconductor substrate and a sapphire substrate are providedrespectively, where a first bonding layer is formed on the semiconductorsubstrate, and a sacrificial layer, a LED die and a second bonding layerare formed successively on the sapphire substrate; then the firstbonding layer and the second bonding layer are bonded; the sacrificiallayer is removed and the sapphire substrate is peeled so that the LEDdie is transferred onto the semiconductor substrate. Since thesemiconductor substrate has a good electrical conductivity, oneelectrode of the LED die may be led out and a groove does not need to beformed. Therefore, the effective lighting area of the LED may beincreased.

Furthermore, the semiconductor substrate may have a better thermalconductivity than the sapphire substrate. Transferring the LED die ontothe semiconductor substrate may be benefit to heat radiation during alight emitting process and enhance the light emitting efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a sectional view of a LED in the priorart;

FIG. 2 schematically illustrates a flow chart of a method for forming aLED according to embodiments of the present disclosure; and

FIG. 3 to FIG. 6 schematically illustrate sectional views ofintermediate structures corresponding to the method for forming a LEDaccording to embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

As described above, a conventional LED die is generally formed on asapphire substrate. Since the material of the sapphire substrate isinsulative, a groove needs to be formed on the LED die so that aconnection electrode may be formed therein, thereby reducing aneffective emitting area.

According to the present disclosure, both a semiconductor substrate anda sapphire substrate are provided. A first bonding layer is formed onthe semiconductor substrate, and a sacrificial layer, a LED die and asecond bonding layer are formed successively on the sapphire substrate.The first and second bonding layers are bonded together. Then thesacrificial layer is removed and the sapphire substrate is peeled sothat the LED die is transferred onto the semiconductor substrate. Sincethe semiconductor substrate has an excellent electrical conductivity,one electrode of the LED die may be led out and a groove does not needto be formed. Therefore, an effective lighting area of the LED may beincreased.

Besides, the semiconductor substrate may have a better thermalconductivity than the sapphire substrate. Transferring the LED die ontothe semiconductor substrate facilitates heat radiation during lightemitting and enhances a light emitting efficiency.

In order to clarify the objects, characteristics and advantages of thedisclosure, embodiments of present disclosure will be described indetail in conjunction with accompanying drawings.

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present disclosure. It will be apparent, however,to those skilled in the art that the present disclosure may be practicedwith other embodiments different from embodiments described below. Thoseskilled in the art can modify and vary the embodiments without departingfrom the spirit and scope of the present disclosure. The presentdisclosure will not be limited to the following embodiments.

FIG. 2 schematically illustrates a flow chart of a method for forming aLED according to embodiments of the present disclosure. The method mayinclude steps of:

Step S21, providing a semiconductor substrate and a sapphire substrate,where a first bonding layer is formed on the semiconductor substrate,and a sacrificial layer, a LED die and a second bonding layer are formedsuccessively on the sapphire substrate;

Step S22, bonding the first bonding layer and the second bonding layer;and

Step S23, removing the sacrificial layer and peeling the sapphiresubstrate.

The method for forming a LED according to embodiments of the presentdisclosure will be described in detail in conjunction with FIG. 2 toFIG. 6.

Referring to FIG. 2 and FIG. 3, Step S21 is executed. In Step S21, botha semiconductor substrate and a sapphire substrate are provided. A firstbonding layer is formed on the semiconductor substrate, and asacrificial layer, a LED die and a second bonding layer are formedsuccessively on the sapphire substrate.

Specifically, a semiconductor substrate 20 is provided, and a firstbonding layer 21 is formed on a surface of the semiconductor substrate20. The semiconductor substrate 20 is made of a semiconductor material,such as monocrystalline silicon, silicon, germanium, gallium arsenide orsilicon germanium compounds. In some embodiments, the semiconductorsubstrate 20 may be an n-doped Si substrate and has a resistivity from0.01Ω·cm to 0.1Ω·cm. The first bonding layer 21 may be made ofpalladium. In a specific embodiment, the first bonding layer 21 made ofpalladium (Pd) may be formed on the surface of the semiconductorsubstrate 20 through a Physical Vapor Deposition (PVD) process. Thefirst bonding layer 21 may have a thickness ranging from 80 nm to 120nm, preferably 100 nm.

A sapphire substrate 30 is provided. The sapphire substrate 30 is mainlymade of Al₂O₃. A first buffer layer 31, a sacrificial layer 32, a LEDdie 33, a contact electrode layer 34 and a second bonding layer 35 areformed successively on a surface of the sapphire substrate 30. The firstbuffer layer 31 is configured to buffer stress and match lattice betweenthe sapphire substrate 30 and the sacrificial layer 32, therebyimproving adhesion therebetween. In some embodiments, the sacrificiallayer 32 may be made of boron phosphide (BP), which may be formedthrough a Metal-Organic Chemical Vapor Deposition (MOCVD) process andhave a thickness ranging from 10 nm to 50 nm. The first buffer layer 31may be made of aluminum nitride (AlN), which may be formed through aMOCVD process and have a thickness ranging from 100 nm to 5000 nm.

The LED die 33 may include a cap layer 33 c, an active layer 33 b and asecond buffer layer 33 a which are formed successively on thesacrificial layer 32. The cap layer 33 c may be made of p-doped galliumnitride. The active layer 33 b may be a multi-quantum well active layerand made of indium gallium nitride. In other embodiments, the activelayer 33 b may be a single-quantum well active layer or other activelayers known to those skilled in the art. The second buffer layer 33 amay be made of n-doped gallium nitride. The cap layer 33 c, the activelayer 33 b and the second buffer layer 33 a may be formed through aMOCVD process.

The contact electrode layer 34 may be made of titanium (Ti), which maybe formed through a PVD process and have a thickness from 2 nm to 10 nm,preferably 5 nm. The contact electrode layer 34 is mainly configured toimprove electrical contact by reducing a contact resistance between thesecond bonding layer 35 and the LED die 33.

The second bonding layer 35 may be a single layer of indium (In) orsilver (Ag), a laminated construction of indium and palladium or alaminated construction of silver and palladium. In some embodiments, thesecond bonding layer 35 may be a laminated construction, including apalladium film 35 b and an indium film 35 a which are formedsuccessively on the contact electrode layer 34. The second bonding layer35 may be formed through a PVD process. The palladium film 35 b may havea thickness ranging from 80 nm to 120 nm, preferably 100 nm. The indiumfilm 35 a may have a thickness ranging from 0.8 μm to 1.2 μm, preferably1 μm.

It should be noted that, the first buffer layer 31 or the contactelectrode layer 34 may be formed optionally. In some embodiments, one ofthem or neither of them may be formed. For example, the sacrificiallayer 32 may be directly formed on the sapphire substrate 30; and thesecond bonding layer 35 may be directly formed on the LED die 33.

Referring to FIG. 2 and FIG. 4, Step S22 is executed. In Step S22, thefirst bonding layer and the second bonding layer are bonded.Specifically, the first bonding layer 21 and the second bonding layer 35are bonded. Thus, the first bonding layer 21 reacts with the secondbonding layer 35 to form a bonding layer 36. In some embodiments, as thefirst bonding layer 21 may be made of palladium and the second bondinglayer 35 may include an indium film 35 a and a palladium film 35 b, thebonding layer 36 is made of palladium indium alloy (PdIn₃). The reactiontemperature may range from 180° C. to 220° C., preferably 200° C. Duringthe bonding process, plasma of nitrogen or other inert gasses may be fedin to reduce the reaction temperature and increase the bonding speed. Insome embodiments, the second bonding layer 35 may be a single layer ofindium and the reaction temperature may range from 180° C. to 220° C.Similarly, plasma of nitrogen or other inert gases may be fed in toreduce the reaction temperature.

Since the second bonding layer 35 is a laminated construction includingthe indium film 35 a and the palladium film 35 b, the indium film 35 ais disposed between the palladium film 35 b and the first bonding layer21 made of palladium during the bonding process. The indium film 35 amay react with the palladium film 35 b and the palladium material in thefirst bonding layer 21 at the same time, thereby further increasing thereaction speed of the bonding process.

In some embodiments, the second bonding layer 35 may be made of a singlelayer of silver or a laminated construction of silver and palladium. Thebonding layer 36 may be made of palladium-silver. The reactiontemperature of silver and palladium may be higher than that of indiumand palladium.

Referring to FIG. 2 and FIG. 5, Step S23 is executed. In Step S23, thesacrificial layer is removed and the sapphire substrate is peeled.Specifically, the sacrificial layer 32 is removed, and the sapphiresubstrate 30 and the first buffer layer 31 are peeled from the LED die33. In some embodiments, the sacrificial layer 32 may be made of boronphosphide. The sacrificial layer 32 may be removed through a dry etchingprocess by using a hydrochloric acid (HCl) gas. The etching process isselective, to have the sacrificial layer 32 removed and other layers notaffected.

Based on the above steps, the LED die 33 is transferred from thesapphire substrate 30 onto the semiconductor substrate 20. One end ofthe LED die 33 is electrically connected to the semiconductor substrate20 through the contact electrode layer 34 and the bonding layer 36. Anegative voltage may be applied to the semiconductor substrate 20 as anegative electrode of the LED. The other end of the LED die 33 isexposed and a positive voltage can be applied to the other end directlyto cause the LED die 33 to emit light. Therefore, there is no need for agroove specially to form an electrode, thus an effective light emittingarea of the LED is increased. Besides, since the semiconductor substrate20 has a much better thermal conductivity than the sapphire substrate30, heat generated during light emitting may release through thesemiconductor substrate 20 in time, thereby avoiding a decrease of alight emitting efficiency due to overheating and enhancing the lightemitting efficiency of the LED.

A LED formed according to embodiments of the present disclosure mayinclude: a semiconductor substrate 20; a bonding layer 36 formed on asurface of the semiconductor substrate 20; a contact electrode layer 34formed on a surface of the bonding layer 36; a LED die 33 formed on asurface of the contact electrode layer 34. The contact electrode layer34 is optional, namely, the LED die 33 may be formed directly on thesurface of the bonding layer 36.

Referring to FIG. 6, following the peeling process, a connectionelectrode 37 may be formed on a surface of the LED die 33, which servesas a positive electrode. The connection electrode 37 may be made of gold(Au), nickel (Ni) or other materials known to those skilled in the art.Furthermore, the semiconductor substrate 20 may be fixed on aninterconnection substrate 38. The interconnection substrate 38 may bemade of aluminum or other conductive metals so that the semiconductorsubstrate 20 is electrically connected to the interconnection substrate38. In practice, multiple LEDs and corresponding peripheral circuits maybe connected together on the interconnection substrate 38 to form alight emitting array.

Therefore, based on FIG. 5, the LED formed according to the embodimentsof the present disclosure may further include: a connection electrode 37formed on the LED die 33 and an interconnection substrate 38electrically connected to the semiconductor substrate 20.

Although the present disclosure has been disclosed as above withreference to preferred embodiments thereof but will not be limitedthereto. Those skilled in the art can modify and vary the embodimentswithout departing from the spirit and scope of the present disclosure.Accordingly, without departing from the scope of the present inventedtechnology scheme, whatever simple modification and equivalent variationbelong to the protection range of the present invented technologyscheme.

What is claimed is:
 1. A light emitting diode, comprising: asemiconductor substrate; a bonding layer formed on a surface of thesemiconductor substrate; and a light emitting diode die formed on asurface of the bonding layer.
 2. The light emitting diode according toclaim 1, where a connection electrode is formed on a surface of thelight emitting diode die.
 3. The light emitting diode according to claim1, where the bonding layer is made of palladium indium alloy orpalladium-silver.
 4. The light emitting diode according to claim 1,further comprising a contact electrode layer formed between the bondinglayer and the light emitting diode die.
 5. The light emitting diodeaccording to claim 4, where the contact electrode layer is made oftitanium.
 6. The light emitting diode according to claim 4, where thecontact electrode layer has a thickness ranging from 2 nm to 10 nm. 7.The light emitting diode according to claim 1, where the light emittingdiode die comprises a buffer layer, an active layer and a cap layerwhich are formed successively on the bonding layer.
 8. The lightemitting diode according to claim 7, where the semiconductor substrateis an n-doped silicon substrate.